In the more than fifty years since the publication of Carl Mannheim's classic essay “Conservative Thought,” a sizable body of literature has come into being concerning the nature of modern European and American conservatism. In this article I propose to review and assess some of the more significant pieces of this literature, to indicate my own views on the nature of conservative thought, and to map out some areas I think students of conserivatism might want to explore further. Such a study of the problem of defining conservatism is, I believe, a worthwhile enterprise, not only because of the intrinsic historical importance of modern conservatism, but also because of the light which our understanding of conservative thought may shed on the development of political theory as a whole during the last two centuries.